Multichamber mill



July 16, 1968 H. SCHMITZ 3,392,924

MULTI CHAMBER MILL Filed May 2, 1966 2 Sheets-Sheet 1 H4 SCHMITZ July16, 1968 MULTICHAMBER MILL 2 Sheets-Sheet i( Filed May 2, 1966 UnitedStates Patent O 3,392,924 MULTICHAMBER MILL Hugo Schmitz, Beckum,Westphalia, Germany, assignor to Klockner-Humboldt-DeutzAktiengesellschaft, Cologne, Germany, a corporation of Germany Fiied May2, 1966, Ser. No. 547,398 Claims priority, application Germany, Apr. 30,1965, Sch 36,968 4 Claims. (Cl. 241-137) My invention relates to amultichamber mill of the tube type having a plurality of grindingchambers rigidly connected to one another and located around a commonrotational axis, the peripheral walls of the mill having no openings.

It is known that particularly `during fine-grinding in tube or cyindermills, the tumbling media, such as metal balls, become loaded with toogreat an amount of kinetic energy. The energy of the tumbling media notemployed for comminuting the charge of working material is transformedinto mechanically produced heat. In many decades of tube milldevelopment history, there has been no lack of endeavor to transform, byspecially subdividing the mill cylinder into a plurality of coaxiallydisposed grinding chambers, at least a portion of the excess energy inthe downwardly turning grinding chamber to driving energy for rotatingthe mill.

A heretofore known embodiment of a multichamber mill has a mill cylinderwhich is divided radially into live chambers. The walls of eachindividual chamber consist of substantially a fifth of the peripheralwall of the mill and two substantially fiat plates disposed with respectto one another so as to define an acute angle. In this manner, thereforelive grinding chambers asymmetrical in cross section are formed. Inaccordance with the asymmetry of the chamber walls with respect to therotational axis of the mill, the displacement of the tumbling media isalso non-uniform or unbalanced. Since the chamber walls are notrotationally symmetrical, it is impossible to have a uniform state ofmotion of the aggregate tumbling media. In the upwardly turning portionof the mill, the flat partition walls serve as raising shovels. Thetumbling media pile up in front of these partition walls so that thepreponderant portion of the quantity of tumbler media is at a standstilland no comminuting action or at least only very little is performedbecause there is substantially no relative motion of the tumbler mediacomponent particles with respect to one another or at best there isrelative motion of only a very small portion of the tumbling mediapellets in the chambers.

In the downwardly turning chamber of these known mills, the quantity oftumbling media is shifted from the flat partition, which serves as thesupporting surface, to the rotationally symmetrical casing of the mill.During the instant in which the downward motion of the grinding chamberstakes places, the potential energy of the tumbling media proper istransformed in part to kinetic energy for the comminuting operation,while the remaining potential energy inures to or is applied to theturning moment of the mill. This reclaimed energy for driving the millopposes the reduced comminuting action 4during the upward motion of thegrinding chamber so that the throughput performance or efficiency isreduced, and the yield of the specific output or eiciency is furthernullified or cancelled in part.

The afore-described known multiple chamber mills have 3,392,924 PatentedJuly 16, 1968 "ice radially extending rotary surfaces or planes whichdiffer from those of the invention in the instant application. If onewere to consider the conditions at the upper apex or crest of thesurfaces, the tumbling media, in contrast to the invention of theinstant application, would be unable to be thrown, as hereinafter noted,relatively far onto the other side of the grinding chamber, but ratherwould accumulate in the angle or corner between both radially extendingsurfaces so that displacement of the center of gravity of the mass oftumbling media to the other side could not occur or could only occur toa small degree. Furthermore, the approximately triangular form of thegrinding chambers in the aforementioned known mills cause the tumblingmedia to accumulate at three locations during rotation of the mill, i.e.in the corners or angles thereof, so that an especially short free slopeor embankment is produced on which the comminuting action in essence iscarried out. Thus the comminuting efciency of these known mills isrelatively small.

It is accordingly an object of my invention to provide multichamber millwhich avoids the aforementioned disadvantages of the heretofore knowndevices and which will enhance the throughput yield or eiciency of themill.

With the foregoing and other objects in view, I provide each of thegrinding chambers, in accordance with my invention, with peripheralwalls comprising a iirst section curved more than and a second sectionspaced from the center of gravity of the cross-sectional plane of thegrinding chamber a distance less than the distance of thefirst-mentioned section from the center of gravity, and both sectionsare so disposed with respect to one another that the section closer tothe gravity center is slipped under the charge or quantity of tumblingmedia when the grinding chambers are moved upwardly.

With the multichamber mill of the invention, the convex sections(unsteady or changing planes) located relatively close to the center ofgravity effect a rotation of the tumbling media approaching the crest ofthe convex sections. This rotation leads to a simultaneous movement ofall the particles in the tumbling media whereby a grinding effect isachieved not only at the sloping surface of the tumbling media but alsoin the entire quantity of tumbling media particles. In this manner,therefore, the grinding eifect is increased. Disregarding that situationin which rotation of the tumbling media occurs, the tumbling media liein the form of a slope or embankment in the vicinity of the grindingchamber section which is curved more than 180 so that a slope is formedthere just as for single-chamber mills and the same comminution effectas in singlechamber mills is achieved. Moreover, the supply of tumblingmedia particles is thrown onto the other side of the respective grindingchamber due to the sudden rotation thereof in the vicinity of the apexof the convex section so that the center of gravity is displaced in thesame direction and the turning moment opposing the drive moment istherewith at least partly balanced or canceled. Furthermore, thetumbling energy of the supply of tumbling media acts in the direction ofthe rotary motion of the grinding chamber so that this energy, insofaras it does not produce comminuting action, is applied toward driving themill.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin multichamber mill, it is nevertheless not intended to be limited tothe details shown, since various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalence of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specic embodiments whenread in connection with the accompanying drawings, in `which FIG. l is alongitudinal section of a multiple chamber mill constructed inaccordance with my invention;

FIGS. 2 and 3 are cross-sectional views taken respectively along thelines II-II and III-III in FIG. 1; and

FIG. 4 is a cross-sectional view similar to that of FIG.

3 of another embodiment of a grinding mill constructed in accordancewith the invention.

As shown in the figures, the multichamber mill constructed in accordancew-ith my invention is provided with four grinding chambers 2a, 2b, 2c,2d, for example, symmetrically disposed about the axis of rotation 1 ofthe mill. Flanges 3a and 3b secure the grinding chamber to the partitionwalls 4a and 4b which are'in turn respectively connected by thecylindrical rings 5a and 5b with the side walls 6a and 6b of the mill.Hollow throat-like trunnions or journals 7a and 7b are located on theend Walls 6a, 6b and are rotatably mounted in bearings 8a and 8b. A gearrim 9 is anged onto the end wall 6a and, by means of meshing pinion 10,which is dri-ven by a non-illustrated drive means, rotates the millabout the axis 1.

The working material which is to be comminuted is conducted through thehopper 11 onto the interior of the hollow cone 12. From the latter, theworking material slides into the space 13 defined by the end wall 6a,the partition 4a, and a conical ring 14 located intermediate to the endlwall 6a and the partition 4a. In the upwardly turning portion of themill, the working material lirst slides against a guide plate 15 (FIG.2), and is then conducted from the latter through the openings 16 intothe grinding chambers. The comminuted material discharges from thegrinding chambers through the openings 17 in i out resulting in anyreduction in the throughput efficiency of the mill. For this purpose, apredominant portion of the chamber walls, in fact the section 21 (FIG.3), is curved more than 180 and is advantageous-ly cylindrically formedso that nearly during the entire rotation, i.e. also in the upwardlymoving grinding chamber, the tumbling media can roll on the walls withvarying velocity just as for a cylindrical mill, so that in thestructure according to the invention there is also relative velocitybetween the particles in the aggregate tumbling media. Thus, in the millconstructed in accordance with my invention, comminuting action is beingcarried out at all times in each grinding chamber, whereas intheraforementioned known grinding mills this occurs predominantly onlyin the downwardly moving grinding chambers. With the embodimentconstructed in accordance with the invention, however, as shown in FIG.3, a further effect is obtained which is based upon the fact that thegrinding chamber walls adjacent the section 21, which is curved morethan 180, has a second section 22 which is spaced from the center ofgravity 23 of the cross-sectional plane of the grinding chamber a lesserdistance than the first-mentioned section 21 is spaced therefrom. Thesecond section 22 (which forms a spatially varying plane) is curved o`rarches into the interior of the grinding chamber and is so located that,during the rotation of the mill in the direction of the arrow 24 withthe upward motion of the grinding chambers, the section 22 graduallyslides under the quantity of tumbling media particles and places theparticles in the vicinity of the apex or crest of the convex section 22.Consequently, a displacement of the static and dynamic centers ofgravity of the quantity of tumbler media and rolling of the tumblingmedia over the wall section 22 then occur. In connection therewith,there is a displacement of a moment in favor of or toward the clockwise`rotating positive turning moment 24. The 'required mill driving poweris thereby reduced. With the rolling of the quantity of tumbler mediaover the convex or arched Wall section 22, the entire quantity oftumbling media is set into motion in a short time, accompanied byslidingmovements within the aggregate tumbling media and a maximum of collisioncontacts. The entire number of collision contacts per unit time isthereby greatly increased as compared to mills of heretofore-knownconstruction. This simultaneously produces a considerable increase inthe specific output of the mill constructed in accordance with theinstant linvention. Furthermore, the tinrrbling energy of thevr-otatedtumbler media components in the rotary direction of the mill produces adecrease in the driving energy necessary for rotating the mill.

A further advantage of the mill'constr'ucted in accordance with theinvention is that the tumbling media particles are partly supported bythe convex or arched wall section 22 during the upward movement of thegrinding chambers whereby it is possible to drive the mill with lessrotary speed than is necessary for the heretofore-known mills. Since thedriving power is proportional to the rotary speed, it follows thereforethat the driving power of the mill constructed in accordance with theinvention must be smaller proportionately as the rotary speed issmaller.

The iigures of the drawing show only examples of preferred embodimentsfor constructing the mill in accordance with the inventive concept ofthe application. Variati-ons thereof are of course possible without inany way reducing the inventive concept and within the scope thereof. Forexample, in FIG. 4 instead of the arched or convex wall section 22, allat wall section 22a in the form of a chord located in the crosssection of the cylindrical chamber Zat-2d can be employed with similarresults. Instead of the ground material outlet 19 at the periphery ofthe mill, an outlet device can be employed equally wherein the groundmaterial discharges from the throatlike trunnion 7b, for example.Furthermore, instead of having only four grinding chambers, it is ofcourse clearly understood that any desired number of chambers can beemployed.

It is also believed to be self-evident that in the empty cross-sectionalspace about the rotary axis 1 of the mill, a screw conveyor can beprovided by means of which either all or a portion of the groundmaterial can be returned from one or more of the grinding chambers againto the mill :inlet end 11 so as to be re-ground.

I claim: v

1. Grinding mill comprising a plurality of rigidly connected grindingchambers adapted to contain a quantity of tumbling media and disposedabout a common rotational axis, said chambers having respective closedperipheral walls each comprising a rst section curved more than and asecond section located closer to the center of gravity -of therespective chamber, in a cross-sec- `tional plane thereof, than saidtrst section, said sections being disposed relative lto one another sothat said second section rides under the quantity of tumbling media inthe respective chamber when said chamber is being moved in an upwarddirection about said' comm-on rotational axrs.

2. Grinding mill according to claim. 1, wherein said first section is atleast partly cylindrical in form.

3. Grinding mill according to claim 1, wherein said second section isconvexly arched in the interior of the respective grinding chamber.

4. Grinding mill according to claim 1, wherein said second section formsa chord extending across a crosssectional plane of the interior of therespective grinding chamber.

References Cited UNITED STATES PATENTS Eggert 241-137 Gibson 241-137 XEppers 241-137 Fries 241--137 X HARRISON L. HINSON, Primary Examiner.

1. GRINDING MILL COMPRISING A PLURALITY OF RIGIDLY CONNECTED GRINDINGCHAMBERS ADAPTED TO CONTAIN A QUANTITY OF TUMBLING MEDIA AND DISPOSEDABOUT A COMMON ROTATIONAL AXIS, SAID CHAMBERS HAVING RESPECTIVE CLOSEDPERIPHERAL WALLS EACH COMPRISING A FIRST SECTION CURVED MORE THAN 180*AND A SECOND SECTION LOCATED CLOSER TO THE CENTER OF GRAVITY OF THERESPECTIVE CHAMBER, IN A CROSS-SECTIONAL PLANE THEREOF, THAN SAID FIRSTSECTION, SAID SECTIONS BEING DISPOSED RELATIVE TO ONE ANOTHER SO THATSAID SECOND SECTION RIDES UNDER THE QUANTITY OF TUMBLING MEDIA IN THERESPECTIVE CHAMBER WHEN SAID CHAMBER IS BEING MOVED IN AN UPWARDDIRECTION ABOUT SAID COMMON ROTATIONAL AXIS.